Apparatus and method for measuring color

ABSTRACT

Color measuring systems and methods are disclosed. Perimeter receiver fiber optics are spaced apart from a central source fiber optic and receive light reflected from the surface of the object being measured. Light from the perimeter fiber optics pass to a variety of filters. The system utilizes the perimeter receiver fiber optics to determine information regarding the height and angle of the probe with respect to the object being measured. Under processor control, the color measurement may be made at a predetermined height and angle. Various color spectral photometer arrangements are disclosed. Translucency, fluorescence and/or surface texture data also may be obtained. Audio feedback may be provided to guide operator use of the system. The probe may have a removable or shielded tip for contamination prevention.

FIELD OF THE INVENTION

[0001] The present invention relates to devices and methods formeasuring the color of objects, and more particularly to devices andmethods for measuring the color of teeth, fabric or other objects orsurfaces with a hand-held probe that presents minimal problems withheight or angular dependencies.

BACKGROUND OF THE INVENTION

[0002] Various color measuring devices such as spectrophotometers andcalorimeters are known in the art. To understand the limitations of suchconventional devices, it is helpful to understand certain principlesrelating to color. Without being bound by theory, Applicants provide thefollowing discussion.

[0003] The color of an object determines the manner in which light isreflected from the surface of the object. When light is incident upon anobject, the reflected light will vary in height, and wavelengthdependent upon the color of the surface of the object. Thus, a redobject will reflect red light with a greater intensity than a blue or agreen object, and correspondingly a green object will reflect greenlight with a greater intensity than a red or blue object.

[0004] One method of quantifying the color of an object is to illuminateit with broad band spectrum or “white” light, and measure the spectralproperties of the reflected light over the entire visible spectrum andcompare the reflected spectrum with the incident light spectrum. Suchinstruments typically require a broad band spectrophotometer, whichgenerally are expensive, bulky and relatively cumbersome to operate,thereby limiting the practical application of such instruments.

[0005] For certain applications, the broad band data provided by aspectrophotometer is unnecessary. For such applications, devices havebeen produced or proposed that quantify color in terms of a numericalvalue or relatively small set of values representative of the color ofthe object.

[0006] It is known that the color of an object can be represented bythree values. For example, the color of an object can be represented byred, green and blue values, an intensity value and color differencevalues, by a CIE value, or by what are known as “tristimulus values” ornumerous other orthogonal combinations. It is important that the threevalues be orthogonal; i.e., any combination of two elements in the setcannot be included in the third element.

[0007] One such method of quantifying the color of an object is toilluminate an object with broad band “white” light and measure theintensity of the reflected light after it has been passed through narrowband filters. Typically three filters (such as red, green and blue) areused to provide tristimulus light values representative of the color ofthe surface. Yet another method is to illuminate an object with threemonochromatic light sources (such as red, green and blue) one at a timeand then measure the intensity of the reflected light with a singlelight sensor. The three measurements are then converted to a tristimulusvalue representative of the color of the surface. Such color measurementtechniques can be utilized to produce equivalent tristimulus valuesrepresentative of the color of the surface. Generally, it does notmatter if a “white” light source is used with a plurality of colorsensors (or a continuum in the case of a spectrophotometer), or if aplurality of colored light sources are utilized with a single lightsensor.

[0008] There are, however, difficulties with the conventionaltechniques. When light is incident upon a surface and reflected to alight receiver, the height of the light sensor and the angle of thesensor relative to the surface and to the light source also affect theintensity of the received light. Since the color determination is beingmade by measuring and quantifying the intensity of the received lightfor different colors, it is important that the height and angulardependency of the light receiver be eliminated or accounted for in somemanner.

[0009] One method for eliminating the height and angular dependency ofthe light source and receiver is to provide a fixed mounting arrangementwhere the light source and receiver are stationary and the object isalways positioned and measured at a preset height and angle. The fixedmounting arrangement greatly limits the applicability of such a method.Another method is to add mounting feet to the light source and receiverprobe and to touch the object with the probe to maintain a constantheight and angle. The feet in such an apparatus must be wide enoughapart to insure that a constant angle (usually perpendicular) ismaintained relative to the object. Such an apparatus tends to be verydifficult to utilize on small objects or on objects that are hard toreach, and in general does not work satisfactorily in measuring objectswith curved surfaces.

[0010] The use of color measuring devices in the field of dentistry hasbeen proposed. In modern dentistry, the color of teeth typically arequantified by manually comparing a patient's teeth with a set of “shadeguides.” There are numerous shade guides available for dentists in orderto properly select the desired color of dental prosthesis. Such shadeguides have been utilized for decades and the color determination ismade subjectively by the dentist by holding a set of shade guides nextto a patient's teeth and attempting to find the best match.Unfortunately, however, the best match often is affected by the ambientlight color in the dental operatory and the surrounding color of thepatient's makeup or clothing and by the fatigue level of the dentist.

[0011] Similar subjective color quantification also is made in the paintindustry by comparing the color of an object with a paint referenceguide. There are numerous paint guides available in the industry and thecolor determination also often is affected by ambient light color, userfatigue and the color sensitivity of the user. Many individuals arecolor insensitive (color blind) to certain colors, further complicatingcolor determination.

[0012] In general, color quantification is needed in many industries.Several, but certainly not all, applications include: dentistry (colorof teeth); dermatology (color of skin lesions); interior decorating(color of paint, fabrics); the textile industry; automotive repair(matching paint colors); photography (color of reproductions, colorreference of photographs to the object being photographed); printing andlithography; cosmetics (hair and skin color, makeup matching); and otherapplications in which it useful to measure color in an expedient andreliable manner.

[0013] With respect to such applications, however, the limitations ofconventional color measuring techniques typically restrict the utilityof such techniques. For example, the high cost and bulkiness of typicalbroad band spectrometers, and the fixed mounting arrangements or feetrequired to address the height and angular dependency, often limit theapplicability of such conventional techniques.

[0014] Moreover, another limitation of such conventional methods anddevices are that the resolution of the height and angular dependencyproblems typically require contact with the object being measured. Incertain applications, it may be desirable to measure and quantify thecolor of an object with a small probe that does not require contact withthe surface of the object. In certain applications, for example,hygienic considerations make such contact undesirable. In the otherapplications such as interior decorating, contact with the object canmar the surface (such as if the object is coated with wet paint) orotherwise cause undesirable effects.

[0015] In summary, there is a need for a low cost, hand-held probe ofsmall size that can reliably measure and quantify the color of an objectwithout requiring physical contact with the object, and also a need formethods based on such a device in the field of dentistry, and otherapplications.

SUMMARY OF THE INVENTION

[0016] In accordance with the present invention, devices and methods areprovided for measuring the color of objects, reliably and with minimalproblems of height and angular dependence. A handheld probe is utilizedin the present invention, with the handheld probe containing a number offiber optics. Light is directed from one (or more) light source fiberoptics towards the object to be measured, which in certain preferredembodiments is a central light source fiber optic (other light sourcearrangements also may be utilized). Light reflected from the object isdetected by a number of light receiver fiber optics. Included in thelight receiver fiber optics are a plurality of perimeter fiber optics.In certain preferred embodiments, three perimeter fiber optics areutilized in order to take measurements at a desired, and predeterminedheight and angle, thereby minimizing height and angular dependencyproblems found in conventional methods. In certain embodiments, thepresent invention also may measure translucence and fluorescencecharacteristics of the object being measured, as well as surface textureand/or other surface characteristics.

[0017] The present invention may include constituent elements of a broadband spectrophotometer, or, alternatively, may include constituentelements of a tristimulus type colorimeter. The present invention mayemploy a variety of color measuring devices in order to measure color ina practical, reliable and efficient manner, and in certain preferredembodiments includes a color filter array and a plurality of colorsensors. A microprocessor is included for control and calculationpurposes. A temperature sensor is included to measure temperature inorder to detect abnormal conditions and/or to compensate for temperatureeffects of the filters or other components of the system. In addition,the present invention may include audio feedback to guide the operatorin making color measurements, as well as one or more display devices fordisplaying control, status or other information.

[0018] With the present invention, color measurements may be made with ahandheld probe in a practical and reliable manner, essentially free ofheight and angular dependency problems, without resorting to fixtures,feet or other undesirable mechanical arrangements for fixing the heightand angle of the probe with respect to the object.

[0019] Accordingly, it is an object of the present invention to addresslimitations of conventional color measuring techniques.

[0020] It is another object of the present invention to provide a methodand device useful in measuring the color of teeth, fabric or otherobjects or surfaces with a hand-held probe of practical size that doesnot require contact with the object or surface.

[0021] It is a further object of the present invention to provide acolor measurement probe and method that does not require fixed positionmechanical mounting, feet or other mechanical impediments.

[0022] It is yet another object of the present invention to provide aprobe and method useful for measuring color that may be utilized with aprobe simply placed near the surface to be measured.

[0023] It is a still further object of the present invention to providea probe and method that are capable of determining translucencycharacteristics of the object being measured.

[0024] It is a further object of the present invention to provide aprobe and method that are capable of determining surface texturecharacteristics of the object being measured.

[0025] It is a still further object of the present invention to providea probe and method that are capable of determining fluorescencecharacteristics of the object being measured.

[0026] Finally, it is an object of the present invention to provide aprobe and method that can measure the area of a small spot singulary, orthat also can measure irregular shapes by moving the probe over an areaand integrating the color of the entire area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention may be more fully understood by adescription of certain preferred embodiments in conjunction with theattached drawings in which:

[0028]FIG. 1 is a diagram illustrating a preferred embodiment of thepresent invention;

[0029]FIG. 2 is a diagram illustrating a cross section of a probe inaccordance with a preferred embodiment of the present invention;

[0030]FIG. 3 is a diagram illustrating an arrangement of fiber opticreceivers and sensors utilized with a preferred embodiment of thepresent invention;

[0031]FIGS. 4A to 4C illustrate certain geometric considerations offiber optics;

[0032]FIGS. 5A and 5B illustrate the light amplitude received by fiberoptic light receivers as a function of height from an object;

[0033]FIG. 6 is a flow chart illustrating a color measuring method inaccordance with an embodiment of the present invention;

[0034]FIGS. 7A and 7B illustrate a protective cap that may be used withcertain embodiments of the present invention;

[0035]FIGS. 8A and 8B illustrate removable probe tips that may be usedwith certain embodiments of the present invention;

[0036]FIG. 9 illustrates a fiber optic bundle in accordance with anotherpreferred embodiment of the present invention;

[0037]FIGS. 10A, 10B, 10C and 10D illustrate and describe other fiberoptic bundle configurations that may be used in accordance with yetother preferred embodiments of the present invention;

[0038]FIG. 11 illustrates a linear optical sensor array that may be usedin certain embodiments of the present invention;

[0039]FIG. 12 illustrates a matrix optical sensor array that may be usedin certain embodiments of the present invention;

[0040]FIGS. 13A and 13B illustrate certain optical properties of afilter array that may be used in certain embodiments of the presentinvention;

[0041]FIGS. 14A and 14B illustrate examples of received lightintensities of receivers used in certain embodiments of the presentinvention; and

[0042]FIG. 15 is a flow chart illustrating audio tones that may be usedin certain preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] The present invention will be described in greater detail withreference to certain preferred embodiments.

[0044] With reference to FIG. 1, an exemplary preferred embodiment of acolor measuring system and method in accordance with the presentinvention will be described.

[0045] Probe tip 1 encloses a plurality of fiber optics, each of whichmay constitute one or more fiber optic fibers. In a preferredembodiment, the fiber optics contained within probe tip 1 includes asingle light source fiber optic and three light receiver fiber optics.The use of such fiber optics to measure the color of an object will bedescribed later herein. Probe tip 1 is attached to probe body 2, onwhich is fixed switch 17. Switch 17 communicates with microprocessor 10through wire 18 and provides, for example, a mechanism by which anoperator may activate the device in order to make a color measurement.Fiber optics within probe tip 1 terminate at the forward end thereof(i.e., the end away from probe body 2). The forward end of probe tip 1is directed towards the surface of the object to be measured asdescribed more fully below. The fiber optics within probe tip 1optically extend through probe body 2 and through fiber optic cable 3 tolight sensors 3, which are coupled to microprocessor 10.

[0046] It should be noted that microprocessor 10 includes conventionalassociated components, such as memory (programmable memory, such asPROM, EPROM or EEPROM; working memory such as DRAMs or SRAMs; and/orother types of memory such as non-volatile memory, such as FLASH),peripheral circuits, clocks and power supplies, although for claritysuch components are not explicitly shown. Other types of computingdevices (such as other microprocessor systems, programmable logic arraysor the like) are used in other embodiments of the present invention.

[0047] In the embodiment of FIG. 1, the fiber optics from fiber opticcable 3 end at splicing connector 4. From splicing connector 4, each orthe three receiver fiber optics used in this embodiment is spliced intoat least five smaller fiber optics (generally denoted as fibers 7),which in this embodiment are fibers of equal diameter, but which inother embodiments may be of unequal diameter (such as a larger orsmaller “height/angle” or perimeter fiber, as more fully describedherein). One of the fibers of each group of five fibers passes to lightsensors 8 through a neutral density filter (as more fully described withreference to FIG. 3), and collectively such neutrally filtered fibersare utilized for purposes of height/angle determination (and also may beutilized to measure surface characteristics, as more fully describedherein). Four of the remaining fibers of each group of fibers passes tolight sensors 8 through color filters and are used to make the colormeasurement. In still other embodiments, splicing connector 4 is notused, and fiber bundles of, for example, five or more fibers each extendfrom light sensors 8 to the forward end of probe tip 1. In certainembodiments, unused fibers or other materials may be included as part ofa bundle of fibers for purposes of, for example, easing themanufacturing process for the fiber bundle. What should be noted isthat, for purposes of the present invention, a plurality of lightreceiver fiber optics (such as fibers 7) are presented to light sensors8, with the light from the light receiver fiber optics representinglight reflected from object 20. While the various embodiments describeherein present tradeoffs and benefits that may not have been apparentprior to the present invention (and thus may be independently novel),what is important for the present discussion is that light from fiberoptics at the forward end of probe tip 1 is presented to color sensors 8for color measurement and angle/height determination, etc.

[0048] Light source 11 in the preferred embodiment is a halogen lightsource (of, for example, 5-100 watts, with the particular wattage chosenfor the particular application), which may be under the control ofmicroprocessor 10. The light from light source 11 reflects from coldmirror 6 and into source fiber optic 5. Source fiber optic 5 passesthrough to the forward end of probe tip 1 and provides the lightstimulus used for purposes of making the measurements described herein.Cold mirror 6 reflects visible light and passes infra-red light, and isused to reduce the amount of infra-red light produced by light source 11before the light is introduced into source fiber optic 5. Such infra-redlight reduction of the light from a halogen source such as light source11 can help prevent saturation of the receiving light sensors, which canreduce overall system sensitivity. Fiber 15 receives light directly fromlight source 11 and passes through to light sensors 8 (which may bethrough a neutral density filter). Microprocessor 10 monitors the lightoutput of light source 11 through fiber 15, and thus may monitor and, ifnecessary compensate for, drift of the output of light source 11. Incertain embodiments, microprocessor 10 also may sound an alarm (such asthrough speaker 16) or otherwise provide some indication if abnormal orother undesired performance of light source 11 is detected.

[0049] The data output from light sensors 8 pass to microprocessor 10.Microprocessor 10 processes the data from light sensors 8 to produce ameasurement of color and/or other characteristics. Microprocessor 10also is coupled to key pad switches 12, which serve as an input device.Through key pad switches 12, the operator may input control informationor commands, or information relating to the object being measured or thelike. In general, key pad switches 12, or other suitable data inputdevices (such as push button, toggle, membrane or other switches or thelike), serve as a mechanism to input desired information tomicroprocessor 10

[0050] Microprocessor 10 also communicates with UART 13, which enablesmicroprocessor 10 to be coupled to an external device such as computer13A. In such embodiments, color data provided by microprocessor 10 maybe processed as desired for the particular application, such as foraveraging, format conversion or for various display or print options,etc. In the preferred embodiment, UART 13 is configured so as to providewhat is known as a RS232 interface, such as is commonly found inpersonal computers.

[0051] Microprocessor 10 also communicates with LCD 14 for purposes ofdisplaying status, control or other information as desired for theparticular application. For example, color bars, charts or other graphicrepresentations of the color or other collected data and/or the measuredobject or tooth may be displayed. In other embodiments, other displaydevices are used, such as CRTs, matrix-type LEDs, lights or othermechanisms for producing a visible indicia of system status or the like.Upon system initialization, for example, LCD 14 may provide anindication that the system is stable, ready and available for takingcolor measurements.

[0052] Also coupled to microprocessor 10 is speaker 16. Speaker 16, in apreferred embodiment as discussed more fully below, serves to provideaudio feedback to the operator, which may serve to guide the operator inthe use of the device. Speaker 16 also may serve to provide status orother information alerting the operator of the condition of the system,including an audio tone, beeps or other audible indication (i.e., voice)that the system is initialized and available for taking measurements.Speaker 16 also may present audio information indicative of the measureddata, shade guide or reference values corresponding to the measureddata, or an indication of the status of the color measurements.

[0053] Microprocessor 10 also receives an input from temperature sensor9. Given that many types of filters (and perhaps light sources or othercomponents) may operate reliably only in a given temperature range,temperature sensor 9 serves to provide temperature information tomicroprocessor 10. In particular, color filters, such as may be includedin light sensors 8, are sensitive to temperature, and operate reliablyonly over a certain temperature range. In certain embodiments, if thetemperature is within a usable range, microprocessor 10 may compensatefor temperature variations of the color filters. In such embodiments,the color filters are characterized as to filtering characteristics as afunction of temperature, either by data provided by the filtermanufacturer, or through measurement as a function of temperature. Suchfilter temperature compensation data may be stored in the form of alook-up table in memory, or may be stored as a set of polynomialcoefficients from which the temperature characteristics of the filtersmay be computed by microprocessor 10.

[0054] In general, under control of microprocessor 10, which may be inresponse to operator activation (through, for example, key pad switches12 or switch 17), light is directed from light source 11, and reflectedfrom cold mirror 6 through source fiber optic 5 (and through fiber opticcable 3, probe body 2 and probe tip 1) and is directed onto object 20.Light reflected from object 20 passes through the receiver fiber opticsin probe tip 1 to light sensors 8 (through probe body 2, fiber opticcable 3 and fibers 7). Based on the information produced by lightsensors 8, microprocessor 10 produces a color measurement result orother information to the operator. Color measurement or other dataproduced by microprocessor 10 may be displayed on display 14, passedthrough UART 13 to computer 13A, or used to generate audio informationthat is presented to speaker 16. Other operational aspects of thepreferred embodiment illustrated in FIG. 1 will be explainedhereinafter.

[0055] With reference to FIG. 2, a preferred embodiment of the fiberoptic arrangement S presented at the forward end of probe tip 1 will nowbe described. As illustrated in FIG. 2, a preferred embodiment of thepresent invention utilizes a single central light source fiber optic,denoted as light source fiber optic S, and a plurality of perimeterlight receiver fiber optics, denoted as light receivers R1, R2 and R3.As is illustrated, a preferred embodiment of the present inventionutilizes three perimeter fiber optics, although in other embodimentstwo, four or some other number of receiver fiber optics are utilized. Asmore fully described herein, the perimeter light receiver fiber opticsserve not only to provide reflected light for purposes of making thecolor measurement, but such perimeter fibers also serve to provideinformation regarding the angle and height of probe tip 1 with respectto the surface of the object that is being measured, and also mayprovide information regarding the surface characteristics of the objectthat is being measured.

[0056] In the illustrated preferred embodiment, receiver fiber optics R1to R3 are positioned symmetrically around source fiber optic S, with aspacing of about 120 degrees from each other. It should be noted thatspacing t is provided between receiver fiber optics R1 to R3 and sourcefiber optic S. While the precise angular placement of the receiver fiberoptics around the perimeter of the fiber bundle in general is notcritical, it has been determined that three receiver fiber opticspositioned 120 degrees apart generally may give acceptable results. Asdiscussed above, in certain embodiments light receiver fiber optics R1to R3 each constitute a single fiber, which is divided at splicingconnector 4 (refer again to FIG. 1), or, in alternate embodiments, lightreceiver fiber optics R1 to R3 each constitute a bundle of fibers,numbering, for example, at least five fibers per bundle. It has beendetermined that, with available fibers of uniform size, a bundle of, forexample, seven fibers may be readily produced (although as will beapparent to one of skill in the art, the precise number of fibers may bedetermined in view of the desired number of receiver fiber optics,manufacturing considerations, etc.). The use of light receiver fiberoptics R1 to R3 to produce color measurements in accordance with thepresent invention is further described elsewhere herein, although it maybe noted here that receiver fiber optics R1 to R3 may serve to detectwhether, for example, the angle of probe tip 1 with respect to thesurface of the object being measured is at 90 degrees, or if the surfaceof the object being measured contains surface texture and/or spectralirregularities. In the case where probe tip 1 is perpendicular to thesurface of the object being measured and the surface of the object beingmeasured is a diffuse reflector, then the light intensity input into theperimeter fibers should be approximately equal. It also should be notedthat spacing t serves to adjust the optimal height at which colormeasurements should be made (as more fully described below), and alsoensures that the light reflected into receiver fiber optics R1 to R3 isat an angle for diffuse reflection, which helps to reduce problemsassociated with measurements of “hot spots” on the surface of the objectbeing measured.

[0057] In one particular aspect of the present invention, area betweenthe fiber optics on probe tip 1 may be wholly or partially filled with anon-reflective material and/or surface (which may be a black mat,contoured or other non-reflective surface). Having such exposed area ofprobe tip 1 non-reflective helps to reduce undesired reflections,thereby helping to increase the accuracy and reliability of the presentinvention.

[0058] With reference to FIG. 3, a partial arrangement of light receiverfiber optics and sensors used in a preferred embodiment of the presentinvention will now be described. Fibers 7 represent light receivingfiber optics, which transmit light reflected from the object beingmeasured to light sensors 8. In a preferred embodiment. sixteen sensors(two sets of eight) are utilized, although for ease of discussion only 8are illustrated in FIG. 3 (in this preferred embodiment, the circuitryof FIG. 3 is duplicated, for example, in order to result in sixteensensors). In other embodiments, other numbers of sensors are utilized inaccordance with the present invention.

[0059] Light from fibers 7 is presented to sensors 8, which in apreferred embodiment pass through filters 22 to sensing elements 24. Inthis preferred embodiment, sensing elements 24 includelight-to-frequency converters, manufactured by Texas Instruments andsold under the part number TSL230. Such converters constitute, ingeneral, photo diode arrays that integrate the light received fromfibers 7 and output an AC signal with a frequency proportional to theintensity (not frequency) of the incident light. Without being bound bytheory, the basic principle of such devices is that, as the intensityincreases, the integrator output voltage rises more quickly, and theshorter the integrator rise time, the greater the output frequency. Theoutputs of the TSL230 sensors are TTL or CMOS compatible digitalsignals, which may be coupled to various digital logic devices.

[0060] The outputs of sensing elements 24 are, in this embodiment,asynchronous signals of frequencies depending upon the light intensitypresented to the particular sensing elements, which are presented toprocessor 26. In a preferred embodiment, processor 26 is a MicrochipPIC16C55 microprocessor, which as described more fully herein implementsan algorithm to measure the frequencies of the signals output by sensingelements 24.

[0061] As previously described, processor 26 measures the frequencies ofthe signals output from sensing elements 24. In a preferred embodiment,processor 26 implements a software timing loop, and at periodicintervals processor 26 reads the states of the outputs of sensingelements 24. An internal counter is incremented each pass through thesoftware timing loop. The accuracy of the timing loop generally isdetermined by the crystal oscillator time base (not shown in FIG. 3)coupled to processor 26 (such oscillators typically are quite stable).After reading the outputs of sensing elements 24, processor 26 performsan exclusive OR (“XOR”) operation with the last data read (in apreferred embodiment such data is read in byte length). If any bit haschanged, the XOR operation will produce a 1, and, if no bits havechanged, the XOR operation will produce a 0. If the result is non-zero,the input byte is saved along with the value of the internal counter(that is incremented each pass through the software timing loop). If theresult is zero, the systems waits (e.g., executes no operationinstructions) the same amount of time as if the data had to be saved,and the looping operation continues. The process continues until alleight inputs have changed at least twice, which enables measurement of afull ½ period of each input. Upon conclusion of the looping process,processor 26 analyzes the stored input bytes and internal counterstates. There should be 2 to 16 saved inputs (for the 8 total sensors ofFIG. 3) and counter states (if two or more inputs change at the sametime, they are saved simultaneously). As will be understood by one orskill in the art, the stored values of the internal counter containsinformation determinative of the period of the signals received fromsensing elements 24. By proper subtraction of internal counter values attimes when an input bit has changed, the period may be calculated. Suchperiods calculated for each of the outputs of sensing elements isprovided by processor 26 to microprocessor 10 (see, e.g., FIG. 1). Fromsuch calculated periods, a measure of the received light intensities maybe calculated.

[0062] It should be noted that the sensing circuitry and methodologyillustrated in FIG. 3 have been determined to provide a practical andexpedient manner in which to measure the light intensities received bysensing elements 24. In other embodiments, other circuits andmethodologies are employed (other exemplary sensing schemes aredescribed elsewhere herein).

[0063] As discussed above with reference to FIG. 1, one of fibers 7measures light source 11, which may be through a neutral density filter,which serves to reduce the intensity of the received light in ordermaintain the intensity roughly in the range of the other received lightintensities. Three of fibers 7 also are from perimeter receiver fiberoptics R1 to R3 (see, e.g., FIG. 2) and also may pass through neutraldensity filters. Such receiving fibers 7 serve to provide data fromwhich angle/height information and/or surface characteristics may bedetermined.

[0064] The remaining twelve fibers (of the preferred embodiment's totalof 16 fibers) of fibers 7 pass through color filters and are used toproduce the color measurement. In a preferred embodiment, the colorfilters are Kodak Sharp Cutting Wratten Gelatin Filters, which passlight with wavelengths greater than the cut-off value of the filter(i.e., redish values), and absorb light with wavelengths less than thecut-off value of the filter (i.e., bluish values). “Sharp Cutting”filters are available in a wide variety of cut-offfrequencies/wavelengths, and the cut-off values generally may beselected by proper selection of the desired cut-off filter. In apreferred embodiment, the filter cut-off values are chosen to cover theentire visible spectrum and, in general, to have band spacings ofapproximately the visible band range (or other desired range) divided bythe number of receivers/filters. As an example, 700 nanometers minus 400nanometers, divided by 11 bands (produced by twelve colorreceivers/sensors), is roughly 30 nanometer band spacing.

[0065] With an array of cut-off filters as described above, and withoutbeing bound by theory or the specific embodiments described herein, thereceived optical spectrum may be measured/calculated by subtracting thelight intensities of “adjacent” color receivers. For example, band 1(400 nm to 430 nm)=(intensity of receiver 12) minus (intensity ofreceiver 11), and so on for the remaining bands. Such an array ofcut-off filters, and the intensity values that may result from filteringwith such an array, are more fully described in connection with FIGS.13A to 14B.

[0066] In a preferred embodiment of the present invention, the specificcharacteristics of the light source, filters, sensors and fiber optics,etc., are normalized/calibrated by directing the probe towards, andmeasuring, a known color standard. Such normalization/calibration may beperformed by placing the probe in a suitable fixture, with the probedirected from a predetermined position (i.e., height and angle) from theknown color standard. Such measured normalization/calibration data maybe stored, for example, in a look-up table, and used by microprocessor10 to normalize or correct measured color or other data. Such proceduresmay be conducted at start-up, at regular periodic intervals, or byoperator command, etc.

[0067] What should be noted from the above description is that thereceiving and sensing fiber optics and circuitry illustrated in FIG. 3provide a practical and expedient way to determine the intensity bycolor of the light reflected from the surface of the object beingmeasured.

[0068] It also should be noted that such a system measures the spectralband of the reflected light from the object, and once measured suchspectral data may be utilized in a variety of ways. For example, suchspectral data may be displayed directly as intensity-wavelength bandvalues. In addition, tristimulus type values may be readily computed(through, for example, conventional matrix math), or any other desiredcolor values. In one particular embodiment useful in dental applications(such as for dental prostheses), the color data is output in the form ofa closest match or matches of dental shade guide value(s). In apreferred embodiment, various existing shade guides (such as the shadeguides produced by Vita Zahnfabrik) are characterized and stored in alook-up table, and the color measurement data are used to select theclosest shade guide value. In still other embodiments, the colormeasurement data are used (such as with look-up tables) to selectmaterials for the composition of paint or ceramics such as forprosthetic teeth. There are many other uses of such spectral datameasured in accordance with the present invention.

[0069] It is known that certain objects such as human teeth mayfluoresce, and such characteristics also may be measured in accordancewith the present invention. A light source with an ultraviolet componentmay be used to produce more accurate color data of such objects. Incertain embodiments, a tungsten/halogen source (such as used in apreferred embodiment) may be combined with a UV light source (such as amercury vapor, xenon or other fluorescent light source, etc.) to producea light output capable of causing the object to fluoresce. Alternately,a separate UV light source, combined with a visible-light-blockingfilter, may be used to illuminate the object. Such a UV light source maybe combined with light from a red LED (for example) in order to providea visual indication of when the UV light is on and also to serve as anaid for the directional positioning of the probe operating with such alight source. A second measurement may be taken using the UV lightsource in a manner analogous to that described earlier, with the band ofthe red LED or other supplemental light source being ignored. The secondmeasurement may thus be used to produce an indication of thefluorescence of the tooth or other object being measured. With such a UVlight source, a silica fiber optic (or other suitable material)typically would be required to transmit the light to the object(standard fiber optic materials such as glass and plastic do notpropagate UV light in a desired manner, etc.).

[0070] As described earlier, the present invention utilizes a pluralityof perimeter receiver fiber optics spaced apart from and around acentral source fiber optic to measure color and determine informationregarding the height and angle of the probe with respect to the surfaceof the object being measured, which may include surface characteristicinformation, etc. Without being bound by theory, a principle underlyingthis aspect of the present invention will now be described withreference to FIGS. 4A to 4C.

[0071]FIG. 4A illustrates a typical step index fiber optic consisting ofa core and a cladding. For this discussion, it is assumed that the corehas an index of refraction of n₀ and the cladding has an index ofrefraction of n₁. Although the following discussion is directed to “stepindex” fibers, it will be appreciated by those of skill in the art thatsuch discussion generally is applicable for gradient index fibers aswell.

[0072] In order to propagate light without loss, the light must beincident within the core of the fiber optic at an angle less than thecritical angle, phi, where phi=Sin⁻¹ {n₁/n₀}, where n₀ is the index ofrefraction of the core and n₁ is the index of refraction of thecladding. Thus, all light must enter the fiber at an angle less than thecritical angle, or it will not be propagated in a desired manner.

[0073] For light entering a fiber optic, it must enter within theacceptance angle phi. Similarly, when the light exits a fiber optic, itwill exit the fiber optic within a cone of angle phi as illustrated inFIG. 4A. The ratio of the index of refraction of the cladding and core{n₁/n₀} is referred to as the aperture of the fiber optic. Typical fiberoptics have an aperture of 0.5, and thus an acceptance/critical angle of60°.

[0074] Consider using a fiber optic as a light source. One end isilluminated by a light source (such as light source 11 of FIG. 1), andthe other is held near a surface. The fiber optic will emit a cone oflight as illustrated in FIG. 4A. If the fiber optic is heldperpendicular to a surface it will create a circular light pattern onthe surface. As the fiber optic is raised, the radius r of the circlewill increase. As the fiber optic is lowered, the radius of the lightpattern will decrease. Thus, the intensity of the light (light energyper unit area) in the illuminated circular area will increase as thefiber optic is lowered and will decrease as the fiber optic is raised.

[0075] The same principle generally is true for a fiber optic beingutilized as a receiver. Consider mounting a light sensor on one end of afiber optic and holding the other end near an illuminated surface. Thefiber optic can only propagate light without loss when the lightentering the fiber optic is incident on the end of the fiber optic nearthe surface if the light enters the fiber optic within its acceptanceangle phi. A fiber optic utilized as a light receiver near a surfacewill only accept and propagate light from the circular area of radius ron the surface. As the fiber optic is raised from the surface, the areaincreases. As the fiber optic is lowered to the surface, the areadecreases.

[0076] Consider two fiber optics parallel to each other as illustratedin FIG. 4B. For simplicity of discussion, the two fiber opticsillustrated are identical in size and aperture. The followingdiscussion, however, generally would be applicable for fiber optics thatdiffer in size and aperture. One fiber optic is a source fiber optic,the other fiber optic is a receiver fiber optic. As the two fiber opticsare held perpendicular to a surface, the source fiber optic emits a coneof light that illuminates a circular area of radius r. The receiverfiber optic can only accept light that is within its acceptance anglephi, or only light that is received within a cone of angle phi. If theonly light available is that emitted by the source fiber optic, then theonly light that can be accepted by the receiver fiber optic is the lightthat strikes the surface at the intersection of the two circles asillustrated in FIG. 4C. As the two fiber optics are lifted from thesurface, the proportion of the intersection of the two circular areasrelative to the circular area of the source fiber optic increases. Asthey near the surface, the proportion of the intersection of the twocircular areas to the circular area of the source fiber optic decreases.If the fiber optics are held too close to the surface, the circularareas will no longer intersect and no light emitted from the sourcefiber optic will be received by the receiver fiber optic.

[0077] As discussed earlier, the intensity of the light in the circulararea illuminated by the source fiber increases as the fiber is loweredto the surface. The intersection of the two cones, however, decreases asthe fiber optic pair is lowered. Thus, as the fiber optic pair islowered to a surface, the total intensity of light received by thereceiver fiber optic increases to a maximal value, and then decreasessharply as the fiber optic pair is lowered still further to the surface.Eventually, the intensity will decrease essentially to zero (assumingthe object being measured is not translucent, as described more fullyherein), and will remain essentially zero until the fiber optic pair isin contact with the surface. Thus, as a source-receiver pair of fiberoptics as described above are positioned near a surface and as theirheight is varied, the intensity of light received by the receiver fiberoptic reaches a maximal value at a critical height h_(c).

[0078] Again without being bound by theory, an interesting property ofthe critical height h_(c) has been observed. The critical height h_(c)is a function primarily of the geometry of fixed parameters, such asfiber apertures, fiber diameters and fiber spacing. Since the receiverfiber optic in the illustrated arrangement is only detecting a maximumvalue and not attempting to quantify the value, its maximum isindependent of the surface characteristics. It is only necessary thatthe surface reflect sufficient light from the intersecting area of thesource and receiver fiber optics to be within the detection range of thereceiver fiber optic light sensor. Thus, red or green or blue or anycolor surface will all exhibit a maximum at the same critical heighth_(c). Similarly, smooth reflecting surfaces and rough surfaces alsowill have varying intensity values at the maximal value, but generallyspeaking all such surfaces will exhibit a maximum at the same criticalheight h_(c). The actual value of the light intensity will be a functionof the color of the surface and of the surface characteristics, but theheight where the maximum intensity value occurs in general will not.

[0079] Although the above discussion has focused on two fiber opticsperpendicular to a surface, similar analysis is applicable for fiberoptic pairs at other angles. When a fiber optic is not perpendicular toa surface, it generally illuminates an elliptical area. Similarly, theacceptance area of a receiver fiber optic generally becomes elliptical.As the fiber optic pair is moved closer to the surface, the receiverfiber optic also will detect a maximal value at a critical heightindependent of the surface color or characteristics. The maximalintensity value measured when the fiber optic pair is not perpendicularto the surface, however, will be less than the maximal intensity valuemeasured when the fiber optic pair is perpendicular to the surface.

[0080] Referring now to FIGS. 5A and 5B, the intensity of light receivedas a fiber optic source-receiver pair is moved to and from a surfacewill now be described. FIG. 5A illustrates the intensity of the receivedlight as a function of time. Corresponding FIG. 5B illustrates theheight of the fiber optic pair from the surface of the object beingmeasured. FIGS. 5A and 5B illustrate (for ease of discussion) arelatively uniform rate of motion of the fiber optic pair to and fromthe surface of the object being measured (although similarillustrations/analysis would be applicable for non-uniform rates aswell).

[0081]FIG. 5A illustrates the intensity of received light as the fiberoptic pair is moved to and then from a surface. While FIG. 5Aillustrates the intensity relationship for a single receiver fiberoptic, similar intensity relationships would be expected to be observedfor other receiver fiber optics, such as, for example, the multiplereceiver fiber optics of FIGS. 1 and 2. In general with the preferredembodiment described above, all fifteen fiber optic receivers (of fibers7) will exhibit curves similar to that illustrated in FIG. 5A.

[0082]FIG. 5A illustrates five regions. In region 1, the probe is movedtowards the surface of the object being measured, which causes thereceived light intensity to increase. In region 2, the probe is movedpast the critical height, and the received light intensity peaks andthen falls off sharply. In region 3, the probe essentially is in contactwith the surface of the object being measured. As illustrated, thereceived intensity in region 3 will vary depending upon the translucenceof the object being measured. If the object is opaque, the receivedlight intensity will be very low, or almost zero (perhaps out of rangeof the sensing circuitry). If the object is translucent, however, thelight intensity will be quite high, but in general should be less thanthe peak value. In region 4, the probe is lifted and the light intensityrises sharply to a maximum value. In region 5, the probe is liftedfurther away from the object, and the light intensity decreases again.

[0083] As illustrated, two peak intensity values (discussed as P1 and P2below) should be detected as the fiber optic pair moves to and from theobject at the critical height h_(c). If peaks P1 and P2 produced by areceive fiber optic are the same value, this generally is an indicationthat the probe has been moved to and from the surface of the object tobe measured in a consistent manner. If peaks P1 and P2 are of differentvalues, then these may be an indication that the probe was not moved toand from the surface of the object in a desired manner, or that thesurface is curved or textured, as described more fully herein. In such acase, the data may be considered suspect and rejected. In addition,peaks P1 and P2 for each of the perimeter fiber optics (see, e.g., FIG.2) should occur at the same critical height (assuming the geometricattributes of the perimeter fiber optics, such as aperture, diameter andspacing from the source fiber optic, etc.). Thus, the perimeter fiberoptics of a probe moved in a consistent, perpendicular manner to andfrom the surface of the object being measured should have peaks P1 andP2 that occur at the same critical height. Monitoring receiver fibersfrom the perimeter receiver fiber optics and looking for simultaneous(or near simultaneous, e.g., within a predetermined range) peaks P1 andP2 provides a mechanism for determining if the probe is held at adesired perpendicular angle with respect to the object being measured.

[0084] In addition, the relative intensity level in region 3 serves asan indication of the level or translucency of the object being measured.Again, such principles generally are applicable to the totality ofreceiver fiber optics in the probe (see. e.g., fibers 7 of FIGS. 1 and3). Based on such principles, measurement techniques in accordance withthe present invention will now be described.

[0085]FIG. 6 is a flow chart illustrating a measuring technique inaccordance with the present invention. Step 49 indicates the start orbeginning of a color measurement. During step 49, any equipmentinitialization, diagnostic or setup procedures may be performed. Audioor visual information or other indicia may be given to the operator toinform the operator that the system is available and ready to take ameasurement. Initiation of the color measurement commences by theoperator moving the probe towards the object to be measured, and may beaccompanied by, for example, activation of switch 17 (see FIG. 1).

[0086] In step 50, the system on a continuing basis monitors theintensity levels for the receiver fiber optics (see, e.g., fibers 7 ofFIG. 1). If the intensity is rising, step 50 is repeated until a peak isdetected. If a peak is detected, the process proceeds to step 52. Instep 52, measured peak intensity P1, and the time at which such peakoccurred, are stored in memory (such as in memory included as a part ofmicroprocessor 10), and the process proceeds to step 54. In step 54, thesystem continues to monitor the intensity levels of the receiver fiberoptics. If the intensity is falling, step 54 is repeated. If a “valley”or plateau is detected (i.e., the intensity is no longer falling, whichgenerally indicates contact or near contact with the object), then theprocess proceeds to step 56. In step 56, the measured surface intensity(IS) is stored in memory, and the process proceeds to step 58. In step58, the system continues to monitor the intensity levels of the receiverfibers. If the intensity is rising, step 58 is repeated until a peak isdetected. If a peak is detected, the process proceeds to step 60. Instep 60, measured peak intensity P2, and the time at which such peakoccurred, are stored in memory, and the process proceeds to step 62. Instep 62, the system continues to monitor the intensity levels of thereceiver fiber optics. Once the received intensity levels begin to fallfrom peak P2, the system perceives that region 5 has been entered (see,e.g., FIG. 5A), and the process proceeds to step 64.

[0087] In step 64, the system, under control of microprocessor 10, mayanalyze the collected data taken by the sensing circuitry for thevarious receiver fiber optics. In step 64, peaks P1 and P2 or one ormore of the various fiber optics may be compared. If any of peaks P1 andP2 for any of the various receiver fiber optics have unequal peakvalues, then the color data may be rejected, and the entire colormeasuring process repeated. Again, unequal values of peaks P1 and P2 maybe indicative, for example, that the probe was moved in anon-perpendicular or otherwise unstable manner (i.e., angular or lateralmovement), and. for example, peak P1 may be representative of a firstpoint on the object. while peak P2 may be representative of a secondpoint on the object. As the data is suspect, in a preferred embodimentof the present invention, color data taken in such circumstances arerejected in step 64.

[0088] If the data are not rejected in step 64, the process proceeds tostep 66. In step 66, the system analyzes the data taken from theneutral-density-filtered receivers from each of the perimeter fiberoptics (e.g., R1 to R3 of FIG. 2). If the peaks of the perimeter fiberoptics did not occur at or about the same point in time, this may beindicative, for example, that the probe was not held perpendicular tothe surface of the object being measured. As non-perpendicular alignmentof the probe with the surface of the object being measured may causesuspect results, in a preferred embodiment of the present invention,color data taken in such circumstances are rejected in step 66. In onepreferred embodiment, detection of simultaneous or near simultaneouspeaking (peaking within a predetermined range of time) serves as anacceptance criterion for the data, as perpendicular alignment generallyis indicated by simultaneous or near simultaneous peaking of theperimeter fiber optics. In other embodiments, step 66 includes ananalysis of peak values P1 and P2 of the perimeter fiber optics. In suchembodiments, the system seeks to determine if the peak values of theperimeter fiber optics (perhaps normalized with any initial calibrationdata) are equal within a defined range. If the peak values of theperimeter fiber optics are within the defined range, the data may beaccepted, and if not. the data may be rejected. In still otherembodiments, a combination of simultaneous peaking and equal valuedetection are used as acceptance/rejection criteria for the color data,and/or the operator may have the ability (such as through key padswitches 12) to control one or more of the acceptance criteria ranges.With such capability, the sensitivity of the system may be controllablyaltered by the operator depending upon the particular application andoperative environment, etc.

[0089] If the data are not rejected in step 66, the process proceeds tostep 68. In step 68, the color data may be processed in a desired mannerto produce output color measurement data. For example, such data may benormalized in some manner, or adjusted based on temperature compensationor other data detected by the system. The data also may be converted todifferent display or other formats, depending on the intended use of thecolor data. In addition, the data indicative of the translucence of theobject also may be quantified and/or displayed in step 68. After step68, the process may proceed to starting step 49, or the process may beterminated, etc.

[0090] In accordance the process illustrated in FIG. 6, three lightintensity values (P1, P2 and PS) are stored per receiver fiber optic tomake color and translucency measurements. If stored peak values P1 andP2 are not equal (for some or all of the receivers), this is anindication that the probe was not held steady over one area, and thedata may be rejected (in other embodiments, the data may not berejected, although the resulting data may be used to produce an averageof the measured color data). In addition, peak values P1 and P2 for thethree neutral density perimeter fiber optics should be equal orapproximately equal; if this is not the case, then this is an indicationthat the probe was not held perpendicular or a curved surface is beingmeasured. In other embodiments, the system attempts to compensate forcurved surfaces and/or non-perpendicular angles. In any event, if thesystem cannot make a color measurement, or if the data is rejectedbecause peak values P1 and P2 are unequal to an unacceptable degree,then the operator is notified so that another measurement or otheraction may be taken (such as adjust the sensitivity).

[0091] With a system constructed and operating as described above, colormeasurements may be taken of an object, with accepted color data havingheight and angular dependencies removed. Data not taken at the criticalheight, or data not taken with the probe perpendicular to the surface ofthe object being measured, etc., are rejected in a preferred embodimentof the present invention. In other embodiments, data received from theperimeter fiber optics may be used to calculate the angle of the probewith respect to the surface of the object being measured, and in suchembodiments non-perpendicular or curved surface color data may becompensated instead of rejected. It also should be noted that peakvalues P1 and P2 for the neutral density perimeter fiber optics providea measure of the luminance (gray value) of the surface of the objectbeing measured, and also may serve to quantify the color value.

[0092] The translucency of the object being measured may be quantifiedas a ratio or percentage, such as, for example, (IS/P1)×100%. In otherembodiments, other methods of quantifying translucency data provided inaccordance with the present invention are utilized.

[0093] In another particular aspect of the present invention, datagenerated in accordance with the present invention may be used toimplement an automated material mixing/generation machine. Certainobjects/materials, such as dental prostheses, are made from porcelain orother powders/materials that may be combined in the correct ratios toform the desired color of the object/prosthesis. Certain powders oftencontain pigments that generally obey Beer's law and/or act in accordancewith Kubelka-Munk equations when mixed in a recipe. Color and other datataken from a measurement in accordance with the present invention may beused to determine or predict desired quantities of pigment or othermaterials for the recipe. Porcelain powders and other materials areavailable in different colors, opacities, etc. Certain objects, such asdental prostheses, may be layered to simulate the degree of translucencyof the desired object (such as to simulate a human tooth). Datagenerated in accordance with the present invention also may be used todetermine the thickness and position of the porcelain or other materiallayers to more closely produce the desired color, translucency, surfacecharacteristics, etc. In addition, based on fluorescence data for thedesired object, the material recipe may be adjusted to include a desiredquantity of fluorescing-type material. In yet other embodiments, surfacecharacteristics (such as texture) information (as more fully describedherein) may be used to add a texturing material to the recipe, all ofwhich may be carried out in accordance with the present invention.

[0094] For more information regarding such pigment-material recipe typetechnology, reference may be made to: “The Measurement of Appearance,”Second Edition, edited by Hunter and Harold, copyright 1987; “Principlesof Color Technology,” by Billmeyer and Saltzman, copyright 1981; and“Pigment Handbook,” edited by Lewis, copyright 1988. All of theforegoing are believed to have been published by John Wiley & Sons,Inc., New York, N.Y., and all of which are hereby incorporated byreference.

[0095] In certain operative environments, such as dental applications,contamination of the probe is of concern. In certain embodiments of thepresent invention, implements to reduce such contamination are provided.

[0096]FIGS. 7A and 7B illustrate a protective cap that may be used tofit over the end of probe tip 1. Such a protective cap consists of body80, the end of which is covered by optical window 82, which in apreferred embodiment consists or a structure having a thin sapphirewindow. In a preferred embodiment, body 80 consists of stainless steel.Body 80 fits over the end of probe tip 1 and may be held into place by,for example, indentations formed in body 80, which fit with ribs 84(which may be a spring clip or other retainer) formed on probe tip 1. Inother embodiments, other methods of affixing such a protective cap toprobe tip 1 are utilized. The protective cap may be removed from probetip 1 and sterilized in a typical autoclave, hot steam or othersterilizing system.

[0097] The thickness of the sapphire window should be less than thecritical height of the probe in order to preserve the ability to detectpeaking in accordance with the present invention. It also is believedthat sapphire windows may be manufactured in a reproducible manner, andthus any light attenuation from one cap to another may be reproducible.In addition, any distortion of the color measurements produced by thesapphire window may be calibrated out by microprocessor 10.

[0098] Similarly, in other embodiments body 80 has a cap with a hole inthe center (as opposed to a sapphire window), with the hole positionedover the fiber optic source/receivers. The cap with the hole serves toprevent the probe from coming into contact with the surface, therebyreducing the risk of contamination.

[0099]FIGS. 8A and 8B illustrate another embodiment of a removable probetip that may be used to reduce contamination in accordance with thepresent invention. As illustrated in FIG. 8A, probe tip 88 is removable,and includes four (or a different number, depending upon theapplication) fiber optic connectors 90, which are positioned withinoptical guard 92. Optical guard 92 serves to prevent “cross talk”between adjacent fiber optics. As illustrated in FIG. 8B, in thisembodiment removable tip 88 is secured in probe tip housing 92 by way ofspring clip 96 (other removable retaining implements are utilized inother embodiments). Probe tip housing 92 may be secured to baseconnector 94 by a screw or other conventional fitting. It should benoted that, with this embodiment, different size tips may be providedfor different applications, and that an initial step of the process maybe to install the properly-sized (or fitted tip) for the particularapplication. Removable tip 88 also may be sterilized in a typicalautoclave, hot steam or other sterilizing system. In addition, theentire probe tip assembly is constructed so that it may be readilydisassembled for cleaning or repair.

[0100] With reference to FIG. 9, a tristimulus embodiment of the presentinvention will now be described. In general, the overall system depictedin FIG. 1 and discussed in detail elsewhere herein may be used with thisembodiment. FIG. 9 illustrates a cross section of the probe tip fiberoptics used in this embodiment.

[0101] Probe tip 100 includes central source fiber optic 106, surroundedby (and spaced apart from) three perimeter receiver fiber optics 104 andthree color receiver fiber optics 102. Three perimeter receiver fiberoptics 104 are optically coupled to neutral density filters and serve asheight/angle sensors in a manner analogous to the embodiment describeabove. Three color receiver fiber optics are optically coupled tosuitable tristimulus filters, such as red, green and blue filters. Withthis embodiment, a measurement may be made of tristimulus color valuesof the object, and the process described with reference to FIG. 6generally is applicable to this embodiment. In particular, perimeterfiber optics 104 may be used to detect simultaneous peaking or otherwisewhether the probe is perpendicular to the object being measured. Inaddition, taking color measurement data at the critical height also maybe used with this embodiment.

[0102]FIG. 10A illustrates an embodiment of the present invention,similar to the embodiment discussed with reference to FIG. 9. Probe tip100 includes central source fiber optic 106, surrounded by (and spacedapart from) three perimeter receiver fiber optics 104 and a plurality ofcolor receiver fiber optics 102. The number of color receiver fiberoptics 102, and the filters associated with such receiver fiber optics102, may be chosen based upon the particular application. As with theembodiment of FIG. 9, the process described with reference to FIG. 6generally is applicable to this embodiment.

[0103]FIG. 10B illustrates an embodiment of the present invention inwhich there are a plurality of receiver fiber optics that surroundcentral source fiber optic 240. The receiver fiber optics are arrangedin rings surrounding the central source fiber optic. FIG. 10Billustrates three rings of receiver fiber optics (consisting of fiberoptics 242, 244 and 246, respectively), in which there are six receiverfiber optics per ring. The rings may be arranged in successive largercircles as illustrated to cover the entire area of the end of the probe,with the distance from each receiver fiber optic within a given ring tothe central fiber optic being equal (or approximately so). Central fiberoptic 240 is utilized as the light source fiber optic and is connectedto the light source in a manner similar to light source fiber optic 5illustrated in FIG. 1.

[0104] The plurality of receiver fiber optics are each coupled to two ormore fiber optics in a manner similar to the arrangement illustrated inFIG. 1 for splicing connector A. One fiber optic from such a splicingconnector for each receiver fiber optic passes through a neutral densityfilter and then to light sensor circuitry similar to the light sensorcircuitry illustrated in FIG. 3. A second fiber optic from the splicingconnector per receiver fiber optic passes through a Sharp CuttingWratten Gelatin Filter and then to light sensor circuitry as discussedelsewhere herein. Thus, each of the receiver fiber optics in the probetip includes both color measuring elements and neutral light measuringor “perimeter” elements.

[0105]FIG. 10D illustrates the geometry of probe 260 (such as describedabove) illuminating an area on flat diffuse surface 272. Probe 260creates light pattern 262 that is reflected diffusely from surface 272in uniform hemispherical pattern 270. With such a reflection pattern,the reflected light that is incident upon the receiving elements in theprobe will be equal (or nearly equal) for all elements if the probe isperpendicular to the surface as described above herein.

[0106]FIG. 10C illustrates a probe illuminating rough surface 263 or asurface that reflects light spectrally. Spectral reflected light willexhibit hot spots or regions where the reflected light intensity isconsiderably greater than it is on other areas. The reflected lightpattern will be uneven when compared to a smooth surface as illustratein FIG. 10D.

[0107] Since a probe as illustrated in FIG. 10B has a plurality ofreceiver fiber optics arranged over a large surface area, the probe maybe utilized to determine the surface texture of the surface as well asbeing able to measure the color and translucency of the surface asdescribed earlier herein. If the light intensity received by thereceiver fiber optics is equal for all fiber optics within a given ringof receiver fiber optics, then generally the surface is diffuse andsmooth. If, however, the light intensity of receiver fibers in a ringvaries with respect to each other, then generally the surface is roughor spectral. By comparing the light intensities measured within receiverfiber optics in a given ring and from ring to ring, the texture andother characteristics of the surface may be quantified.

[0108]FIG. 11 illustrates an embodiment of the present invention inwhich linear optical sensors and a color gradient filter are utilizedinstead of light sensors 8 (and filters 22, etc.). Receiver fiber optics7, which may be optically coupled to probe tip 1 as with the embodimentof FIG. 1, are optically coupled to linear optical sensor 112 throughcolor gradient filter 110. In this embodiment, color gradient filter 110may consist of series of narrow strips of cut-off type filters on atransparent or open substrate, which are constructed so as topositionally correspond to the sensor areas of linear optical sensor112. A sample of a commercially available linear optical sensor 112 isTexas Instruments part number TSL213, which has 61 photo diodes in alinear array. Light receiver fiber optics 7 are arranged correspondinglyin a line over linear optical sensor 112. The number of receiver fiberoptics may be chosen for the particular application, so long as enoughare included to more or less evenly cover the full length of colorgradient filter 110. With this embodiment, the light is received andoutput from receiver fiber optics 7, and the light received by linearoptical sensor 112 is integrated for a short period of time (determinedby the light intensity, filter characteristics and desired accuracy).The output of linear array sensor 112 is digitized by ADC 114 and outputto microprocessor 116 (which may the same processor as microprocessor 10or another processor).

[0109] In general, with the embodiment of FIG. 11, perimeter receiverfiber optics may be used as with the embodiment of FIG. 1, and ingeneral the process described with reference to FIG. 6 is applicable tothis embodiment.

[0110]FIG. 12 illustrates an embodiment of the present invention inwhich a matrix optical sensor and a color filter grid are utilizedinstead of light sensors 8 (and filters 22, etc.). Receiver fiber optics7, which may be optically coupled to probe tip 1 as with the embodimentof FIG. 1, are optically coupled to matrix optical sensor 122 throughfilter grid 120. Filter grid 120 is a filter array consisting of anumber of small colored spot filters that pass narrow bands of visiblelight. Light from receiver fiber optics 7 pass through correspondingfilter spots to corresponding points on matrix optical sensor 122. Inthis embodiment, matrix optical sensor 122 may be a monochrome opticalsensor array, such as CCD-type or other type of light sensor elementsuch as may be used in a video camera. The output of matrix opticalsensor 122 is digitized by ADC 124 and output to microprocessor 126(which may the same processor as microprocessor 10 or anotherprocessor). Under control of microprocessor 126, matrix optical sensor126 collects color data from receiver fiber optics 7 through colorfilter grid 120.

[0111] In general, with the embodiment of FIG. 12, perimeter receiverfiber optics may be used as with the embodiment of FIG. 1, and ingeneral the process described with reference to FIG. 6 also isapplicable to this embodiment.

[0112] As will be clear from the foregoing description, with the presentinvention a variety of types of spectral color photometers (ortristimulus-type calorimeters) may be constructed, with perimeterreceiver fiber optics used to collect color data essentially free fromheight and angular deviations. In addition, in certain embodiments, thepresent invention enables color measurements to be taken at a criticalheight from the surface of the object being measured, and thus colordata may be taken without physical contact with the object beingmeasured (in such embodiments, the color data is taken only by passingthe probe through region 1 and into region 2, but without necessarilygoing into region 3 of FIGS. 5A and 5B). Such embodiments may beutilized if contact with the surface is undesirable in a particularapplication. In the embodiments described earlier, however, physicalcontact (or near physical contact) of the probe with the object mayallow all five regions of FIGS. 5A and 5B to be utilized, therebyenabling color measurements to be taken such that translucencyinformation also may be obtained. Both types of embodiments generallyare within the scope of the invention described herein.

[0113] Additional description will now be provided with respect tocut-off filters of the type described in connection with the preferredembodiment(s) of FIGS. 1 and 3 (such as filters 22 of FIG. 3). FIG. 13Aillustrates as properties of a single Kodak Sharp Cutting WrattenGelatin Filter discussed in connection with FIG. 3. Such a cut-offfilter passes light below a cut-off frequency (i.e., above a cut-offwavelength). Such filters may be manufactured to have a wide range ofcut-off frequencies/wavelengths. FIG. 13B illustrates a number of suchfilters, twelve in a preferred embodiment, with cut-offfrequencies/wavelengths chosen so that essentially the entire visibleband is covered by the collection of cut-off filters.

[0114]FIGS. 14A and 14B illustrate exemplary intensity measurementsusing a cut-off filter arrangement such as illustrated in FIG. 13B,first in the case of a white surface being measured (FIG. 14A), and alsoin the case of a blue surface being measured (FIG. 14B). As illustratedin FIG. 14A, in the case of a white surface, the neutrally filteredperimeter fiber optics, which are used to detect height and angle, etc.,generally will produce the highest intensity (although this depends atleast in part upon the characteristics of the neutral density filters).As a result of the stepped cut-off filtering provided by filters havingthe characteristics illustrated in FIG. 13B, the remaining intensitieswill gradually decrease in value as illustrated in FIG. 14A. In the caseof a blue surface, the intensities will decrease in value generally asillustrated in FIG. 14B. Regardless of the surface, however, theintensities out of the filters will always decrease in value asillustrated, with the greatest intensity value being the output of thefilter having the lowest wavelength cut-off value (i.e., passes allvisible light up to blue), and the lowest intensity value being theoutput of the filter having the highest wavelength cut-off (i.e., passesonly red visible light). As will be understood from the foregoingdescription, any color data detected that does not fit the decreasingintensity profiles of FIGS. 14A and 14B may be detected as anabnormality, and in certain embodiments detection of such a conditionresults in data rejection generation of an error message or initiationof a diagnostic routine, etc.

[0115] Reference should be made to the FIGS. 1 and 3 and the relateddescription for a detailed discussion of how such a cut-off filterarrangement may be utilized in accordance with the present invention.

[0116]FIG. 15 is a flow chart illustrating audio tones that may be usedin certain preferred embodiments of the present invention. It has beendiscovered that audio tones (such as tones, beeps, voice or the likesuch as will be described) present a particularly useful and instructivemeans to guide an operator in the proper use of a color measuring systemof the type described herein.

[0117] The operator may initiate a color measurement by activation of aswitch (such as switch 17 of FIG. 1) at step 150. Thereafter, if thesystem is ready (set-up, initialized, calibrated, etc.), alower-the-probe tone is emitted (such as through speaker 16 of FIG. 1)at step 152. The system attempts to detect peak intensity P1 at step154. If a peak is detected, at step 156 a determination is made whetherthe measured peak P1 meets the applicable criteria (such as discussedabove in connection with FIGS. 5A, 5B and 6). If the measured peak P1 isaccepted, a first peak acceptance tone is generated at step 160. If themeasured peak P1 is not accepted, an unsuccessful cone is generated atstep 158, and the system may await the operator to initiate a furthercolor measurement. Assuming that the first peak was accepted, the systemattempts to detect peak intensity P2 at step 162. If a second peak isdetected, at step 164 a determination is made whether the measured peakP2 meets the applicable criteria. If the measured peak P2 is acceptedthe process proceeds to color calculation step 166 (in otherembodiments, a second peak acceptance tone also is generated at step166). If the measured peak P2 is not accepted, an unsuccessful tone isgenerated at step 158, and the system may await the operator to initiatea further color measurement. Assuming that the second peak was accepted,a color calculation is made at step 166 (such as, for example,microprocessor 10 of FIG. 1 processing the data output from lightsensors 8, etc.). At step 168, a determination is made whether the colorcalculation meets the applicable criteria. If the color calculation isaccepted, a successful tone is generated at step 170. If the colorcalculation is not accepted, an unsuccessful tone is generated at step158, and the system may await the operator to initiate a further colormeasurement.

[0118] With unique audio tones presented to an operator in accordancewith the particular operating state of the system, the operator's use ofthe system may be greatly facilitated. Such audio information also tendsto increase operator satisfaction and skill level, as, for example,acceptance tones provide positive and encouraging feedback when thesystem is operated in a desired manner.

[0119] As will be apparent to those skilled in the art, certainrefinements may be made in accordance with the present invention. Forexample, a central light source fiber optic is utilized in certainpreferred embodiments, but other light source arrangements (such as aplurality of light source fibers, etc.). In addition, lookup tables areutilized for various aspects of the present invention, but polynomialtype calculations could similarly be employed. Thus, although variouspreferred embodiments of the present invention have been disclosed forillustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and/or substitutions are possiblewithout departing from the scope and spirit of the present invention asdisclosed in the claims.

[0120] Reference is also made to copending application Ser. No. ______,filed Jan. 2, 1996, for “Apparatus and Method for Measuring the Color ofTeeth,” by the inventors hereof, which is hereby incorporated byreference.

What is claimed is:
 1. An apparatus for measuring the color of an objectwith a probe as the probe is moved with respect to the object,comprising: a probe having a central source fiber optic and a pluralityof receiver fiber optics spaced apart from the central source fiberoptic, wherein light from the central source fiber optic reflects intothe plurality of receiver fiber optics; sensors coupled to receive lightfrom the receiver fibers, wherein at least some of sensors measure thevalue of the intensity of light in predetermined color bands; aprocessor coupled to receive data from the light sensors; wherein theprocessor monitors the intensity values for one or more of the receiverfiber optics and stores data from the sensors at time when the one ormore receiver fiber optics simultaneously have a peak intensity value.